Conductive composition exhibiting PTC behavior and over-current protection device using the same

Abstract

The present invention discloses a conductive composition comprising a plurality of polymers and at least one conductive filler. The polymers are compatible under a molecular size and the form of the conductive filler includes a flake. The conductive composition of the present invention owns better electrical characteristics than a conventional conductive composition that comprises a single polymer. The present invention further discloses an over-current protection device comprising two metal foils and a PTC (positive temperature coefficient; PTC) composition layer. The PTC composition layer contains the conductive composition.

1 . A conductive composition exhibiting PTC behavior, comprising: 
 a plurality of polymers, which are compatible under a molecular size; and    at least one conductive filler dispersed in the polymers, wherein the form of the conductive filler includes a flake.    
   
   
       2 . The conductive composition of  claim 1 , further comprising a coupling agent that improves the resistance uniformity and processibility of the conductive composition.  
   
   
       3 . The conductive composition of  claim 1 , wherein the polymers are selected from the group consisting of epoxy resin, polyethylene, high-density polyethylene, polyoctylene, polypropylene, carboxylic resin and its copolymer or the mixture thereof.  
   
   
       4 . The conductive composition of  claim 1 , wherein the conductive filler is selected from the group consisting of carbon black, metal and ceramic materials.  
   
   
       5 . The conductive composition of  claim 1 , wherein the conductive filler is a mixture of nickel powder and carbon black.  
   
   
       6 . The conductive composition of  claim 5 , wherein the volume percentage of the nickel powder is from 23% to 33%.  
   
   
       7 . The conductive composition of  claim 5 , wherein the volume percentage of the carbon black is from 5% to 25%.  
   
   
       8 . The conductive composition of  claim 2 , wherein the volume percentage of the coupling agent is from 0% to 5%.  
   
   
       9 . An over-current protection device, comprising: 
 two metal foils; and    a PTC composition layer, which comprises: 
 a plurality of polymers, which are compatible under a molecular size; and  
 at least one conductive filler dispersed in the polymers, wherein the form of the conductive filler includes a flake.  
   
   
   
       10 . The over-current protection device of  claim 9 , wherein the polymers are selected from the group consisting of epoxy resin, polyethylene, high-density polyethylene, polyoctylene, polypropylene, carboxylic resin and its copolymer or the mixture thereof.  
   
   
       11 . The over-current protection device of  claim 9 , wherein the conductive filler is selected from the group consisting of carbon black, metal and ceramic materials.  
   
   
       12 . The over-current protection device of  claim 9 , wherein the conductive filler is a mixture of nickel powder and carbon black.